Thick Outer Cover Layer Golf Ball

ABSTRACT

A golf ball including a low compression core having an outer surface and a geometric center and being formed from a substantially homogenous composition throughout, the core having a diameter of 1.18 inches to 1.40 inches, an Atti compression of 42 or less, and a coefficient of restitution of 0.750 to 0.790. An outer cover having a thickness of 0.14 inches to 0.16 inches and a Shore D hardness of 60 to 70 is disposed about the core. The outer surface has a first hardness and the geometric center has a second hardness, the first hardness being substantially the same as or lower than the second hardness to define a “negative” hardness gradient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/039,224, filed Feb. 28, 2008, which is acontinuation-in-part of U.S. patent application Ser. No. 11/829,461,filed Jul. 27, 2007, which is a continuation-in-part of U.S. patentapplication Ser. No. 11/772,903, filed Jul. 3, 2007, and also acontinuation-in-part of co-pending U.S. patent application Ser. No.11/469,059, filed Aug. 31, 2006, which is a continuation of co-pendingU.S. patent application Ser. No. 11/267,487, filed Nov. 4, 2005 and nowU.S. Pat. No. 7,150,687, which is a continuation of co-pending U.S.patent application Ser. No. 10/841,031, filed May 7, 2004 and now U.S.Pat. No. 7,004,856.

FIELD OF THE INVENTION

This invention relates generally to golf balls containing cores, moreparticularly single-layer cores, having a surface hardness equal to orless than the center hardness to define a “negative” hardness gradientacross the core.

BACKGROUND OF THE INVENTION

Golf balls have been designed to provide particular playingcharacteristics. These characteristics generally include initial ballvelocity, coefficient of restitution (COR), compression, weightdistribution and spin of the golf ball, which can be optimized forvarious types of players.

Generally, the hardness of a golf ball or a golf ball core is one ofmany factors used in designing golf balls. Typically, when a golf ballis hard, e.g., possessing a high compression value and low deformation,it typically has high COR and high initial velocity after impact with agolf club. However, a hard golf ball has a firm feel and can bedifficult to control around the greens. A softer golf ball, e.g., havinga lower compression value and high deformation, feels better and iseasier to control with short iron clubs for greenside play.

Recent advancements in golf ball design can produce golf balls with thecombination of low compression for soft “feel” and high COR for longflight distance. The COR for low compression golf balls, however,decreases at higher impact speed with golf clubs.

Solid golf balls are typically made with a solid core encased by acover, both of which can have multiple layers, such as a dual corehaving a solid center and an outer core layer, or a multi-layer coverhaving an inner. Generally, golf ball cores and/or centers areconstructed with a thermoset rubber, typically a polybutadiene-basedcomposition. The cores are usually heated and crosslinked to createcertain characteristics, such as higher or lower compression, which canimpact the spin rate of the ball and/or provide better “feel.” These andother characteristics can be tailored to the needs of golfers ofdifferent abilities. From the perspective of a golf ball manufacturer,it is desirable to have cores exhibiting a wide range of properties,such as resilience, durability, spin, and “feel,” because this enablesthe manufacturer to make and sell many different types of golf ballssuited to differing levels of ability.

Heretofore, most single core golf ball cores have had a conventionalhard-to-soft hardness gradient from the surface of the core to thecenter of the core, otherwise known as a “positive hardness gradient.”The patent literature contains a number of references that discuss ahard-surface-to-soft-center hardness gradient across a golf ball core.

U.S. Pat. No. 4,650,193 to Molitor et al. generally discloses a hardnessgradient in the surface layers of a core by surface treating a slug ofcurable elastomer with a cure-altering agent and subsequently moldingthe slug into a core. This treatment allegedly creates a core with twozones of different compositions, the first part being the hard,resilient, central portion of the core, which was left untreated, andthe second being the soft, deformable, outer layer of the core, whichwas treated by the cure-altering agent. The two “layers” or regions ofthe core are integral with one another and, as a result, achieve theeffect of a gradient of soft surface to hard center.

U.S. Pat. No. 3,784,209 to Berman, et al. generally discloses asoft-to-hard hardness gradient. The '209 patent discloses anon-homogenous, molded golf ball with a core of “mixed” elastomers. Acenter sphere of uncured elastomeric material is surrounded by acompatible but different uncured elastomer. When both layers ofelastomer are concurrently exposed to a curing agent, they becomeintegral with one another, thereby forming a mixed core. The center ofthis core, having a higher concentration of the first elastomericmaterial, is harder than the outer layer. One drawback to this method ofmanufacture is the time-consuming process of creating first elastomerand then a second elastomer and then molding the two together.

Other patents discuss cores that receive a surface treatment to providea soft ‘skin’. However, since the interior portions of these cores areuntreated, they have the similar hard surface to soft center gradient asconventional cores. For example, U.S. Pat. No. 6,113,831 to Nesbitt etal. generally discloses a conventional core and a separate soft skinwrapped around the core. This soft skin is created by exposing thepreform slug to steam during the molding process so that a maximum moldtemperature exceeds a steam set point, and by controlling exothermicmolding temperatures during molding. The skin comprises theradially-outermost 1/32 inch to ¼ inch of the spherical core. U.S. Pat.Nos. 5,976,443 and 5,733,206, both to Nesbitt et al., disclose theaddition of water mist to the outside surface of the slug before moldingin order to create a soft skin. The water allegedly softens thecompression of the core by retarding crosslinking on the core surface,thereby creating an even softer soft skin around the hard centralportion.

Additionally, a number of patents disclose multilayer golf ball cores,where each core layer has a different hardness thereby creating ahardness gradient from core layer to core layer.

There remains a need, however, to achieve a single layer core that has asoft-to-hard gradient (a “negative” hardness gradient), from the surfacetowards the center, and to achieve a method of producing such a corethat is inexpensive and efficient. A core exhibiting suchcharacteristics would allow the golf ball designer to create productswith unique combinations of compression, “feel,” and spin.

SUMMARY OF THE INVENTION

The present invention is directed to a golf ball including a core havingan outer surface and a geometric center. The core is preferably entirelyformed from a substantially homogenous composition and has a diameter of1.20 inches or less, a compression of 45 or less, and a coefficient ofrestitution of 0.780 or greater when measured at an incoming velocity of125 ft/s. The core is typically covered with an outer cover layer havinga thickness of 0.14 inches or greater and having a Shore D hardness of60 to 70. The outer surface of the core is preferably substantially thesame as or lower than the hardness of the geometric center of the coreto define a “negative” hardness gradient.

The homogeneous composition may also include a soft and fast agent. Thehardness of the geometric center is typically about 0 Shore C to about 5Shore C higher than the hardness of the outer surface of the core.Additionally, the core has a maximum hardness value and the hardness ofthe geometric center of the core has less than about 10 Shore Cdifference from the maximum hardness value, more preferably less thanabout 5 Shore C from the maximum hardness value.

The present invention is also directed to a golf ball that includes acore that has a substantially homogenous composition throughout, anouter surface, and a geometric center. The core has an outer diameter of1.40 inches or less, a compression of 60 or less, and a coefficient ofrestitution of 0.780 or greater when measured at an incoming velocity of125 ft/s. The golf ball also has an outer cover around the core having athickness of 0.101 inches to 0.25 inches. The geometric center of thecore has a first hardness value, the outer surface of the core has asecond hardness value, and the core has a maximum hardness value, suchthat the first hardness is substantially the same as or higher than thesecond hardness to define a “negative” hardness gradient, and has lessthan about 10 Shore C difference from the maximum hardness of the core.

The first hardness is preferably less than about 5 Shore C lower thanthe maximum hardness. The second hardness is preferably about 0 Shore Cto about 10 Shore C lower than the first hardness, more preferably about0 Shore C to about 5 Shore C lower than the first hardness. The golfball has a coefficient of restitution of 0.810 to 0.825 when measured atan incoming velocity of 125 ft/s. The cover thickness is 0.125 inches to0.2 inches. In a preferred embodiment, the composition further includesa soft and fast agent

The present invention is further directed to a golf ball comprising acore having a substantially homogenous thermoset rubber compositionthroughout, an outer surface having a first hardness, and a centerhaving a second hardness, the first hardness being substantially thesame as or lower than the second hardness to define a negative hardnessgradient; and an outer cover having a thickness of 0.1 inches orgreater; wherein the core comprises a diene rubber composition, has anouter diameter of 1.40 inches or less, a compression of 70 or less, anda coefficient of restitution of 0.770 or greater when measured at anincoming velocity of 125 ft/s, and wherein the golf ball has acompression of 75 to 110 and a coefficient of restitution of 0.810 orgreater when measured at an incoming velocity of 125 ft/s.

The core has a diameter of 0.5 inches to 1.4 inches and a compression of60 or less, more preferably 50 or less. The core has a maximum hardnessvalue and the hardness of the center of the core is less than about 5Shore C lower than the maximum hardness. The hardness of the center ofthe core is preferably about 0 Shore C to about 10 Shore C lower thanthe hardness of the core surface, more preferably about 0 Shore C toabout 5 Shore C lower than the hardness of the core surface. The coverhas a hardness of 70 Shore D or less and a thickness of 0.115 inches to0.25 inches.

Definitions

The following terms that are used in this application are defined interms of the enumerated ASTM tests: Specific Gravity ASTM D-792,Flexural Modulus ASTM D-790, Shore D Hardness ASTM D-2240, and Shore CHardness ASTM D-2240. The ASTM D-792 test was carried out in labconditions where the temperature was controlled to 20-23° C.

As used herein, the terms “points” and “compression points” refer to thecompression scale or the compression scale based on the ATTI EngineeringCompression Tester. This scale, which is well known to those working inthis field, is used in determining the relative compression of a core orball. Compression is measured by applying a spring-loaded force to thegolf ball center, golf ball core or the golf ball to be examined, with amanual instrument (an “Atti gauge”) manufactured by the Atti EngineeringCompany of Union City, N.J. This machine, equipped with a Federal DialGauge, Model D81-C, employs a calibrated spring under a known load. Thesphere to be tested is forced a distance of 0.2 inches (5 mm) againstthis spring. If the spring, in turn, compresses 0.2 inches, thecompression is rated at 100; if the spring compresses 0.1 inches, thecompression value is rated as 0. Thus more compressible, softermaterials will have lower Atti gauge values than harder, lesscompressible materials. Compression measured with this instrument isalso referred to as PGA compression.

As used herein, “COR” refers to Coefficient of Restitution, which isobtained by dividing a ball's rebound velocity by its initial (i.e.,incoming) velocity. This test is performed by firing the samples out ofan air cannon at a vertical steel plate over a range of test velocities(from 75 to 150 ft/s). A golf ball having a high COR dissipates asmaller fraction of its total energy when colliding with the plate andrebounding therefrom than does a ball with a lower COR. Unless otherwisenoted, the COR values reported herein are the values determined at anincoming velocity of 125 ft/s.

As used herein, the term “copolymer” refers to a polymer which is formedfrom two or more monomers, wherein the monomers are not identical.

As used herein, the term “terpolymer” refers to a polymer which isformed from three monomers, wherein the monomers are not identical.

As used herein, the term “fillers” includes any compound or compositionthat can be used to vary the density and other properties of the subjectgolf ball cores.

As used herein, the term “pph” in connection with a batch formulationrefers to parts by weight of the constituent per hundred parts of thebase composition (e.g., elastomer).

As used herein, the term “Mooney viscosity” refers to the unit used tomeasure the plasticity of raw or unvulcanized rubber. The plasticity ina Mooney unit is equal to the torque, measured on an arbitrary scale, ona disk in a vessel that contains rubber at a temperature of 100° C. androtates at two revolutions per minute. The measurement of Mooneyviscosity is defined according to ASTM D-1646.

The term “about,” as used herein in connection with one or more numbersor numerical ranges, should be understood to refer to all such numbers,including all numbers in a range.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The balls of the present invention may include a single-layer(one-piece) golf ball, and multi-layer golf balls, such as one having acore and a cover surrounding the core, but are preferably formed from acore comprised of a solid center (otherwise known as an inner core) andan outer core layer, an inner cover layer and an outer cover layer. Ofcourse, any of the core and/or the cover layers may include more thanone layer. In a preferred embodiment, the core is formed of an innercore and an outer core layer where both the inner core and the outercore layer have a “soft-to-hard” hardness gradient (a “negative”hardness gradient) radially inward from each component's outer surfacetowards its innermost portion (i.e., the center of the inner core or theinner surface of the outer core layer), although alternative embodimentsinvolving varying direction and combination of hardness gradient amongstcore components are also envisioned (e.g., a “negative” gradient in thecenter coupled with a “positive” gradient in the outer core layer, orvice versa).

The center of the core may also be a liquid-filled or hollow spheresurrounded by one or more intermediate and/or cover layers, or it mayinclude a solid or liquid center around which tensioned elastomericmaterial is wound. Any layers disposed around these alternative centersmay exhibit the inventive core hardness gradient (i.e., “negative”). Thecover layer may be a single layer or, for example, formed of a pluralityof layers, such as an inner cover layer and an outer cover layer.

As briefly discussed above, the inventive cores may have a hardnessgradient defined by hardness measurements made at the surface of theinner core (or outer core layer) and radially inward towards the centerof the inner core, typically at 2-mm increments. As used herein, theterms “negative” and “positive” refer to the result of subtracting thehardness value at the innermost portion of the component being measured(e.g., the center of a solid core or an inner core in a dual coreconstruction; the inner surface of a core layer; etc.) from the hardnessvalue at the outer surface of the component being measured (e.g., theouter surface of a solid core; the outer surface of an inner core in adual core; the outer surface of an outer core layer in a dual core,etc.). For example, if the outer surface of a solid core has a lowerhardness value than the center (i.e., the surface is softer than thecenter), the hardness gradient will be deemed a “negative” gradient (asmaller number−a larger number=a negative number). It is preferred thatthe inventive cores have a zero or a negative hardness gradient, morepreferably between zero (0) and −10, most preferably between 0 and −5.

Preferably, the core layers (inner core or outer core layer) is madefrom a composition including at least one thermoset base rubber, such asa polybutadiene rubber, cured with at least one peroxide and at leastone reactive co-agent, which can be a metal salt of an unsaturatedcarboxylic acid, such as acrylic acid or methacrylic acid, anon-metallic coagent, or mixtures thereof. Preferably, a suitableantioxidant is included in the composition. An optional soft and fastagent (and sometimes a cis-to-trans catalyst), such as an organosulfuror metal-containing organosulfur compound, can also be included in thecore formulation.

Other ingredients that are known to those skilled in the art may beused, and are understood to include, but not be limited to,density-adjusting fillers, process aides, plasticizers, blowing orfoaming agents, sulfur accelerators, and/or non-peroxide radicalsources. The base thermoset rubber, which can be blended with otherrubbers and polymers, typically includes a natural or synthetic rubber.A preferred base rubber is 1,4-polybutadiene having a cis structure ofat least 40%, preferably greater than 80%, and more preferably greaterthan 90%.

Examples of desirable polybutadiene rubbers include BUNA® E CB22 andBUNA® CB23, commercially available from LANXESS Corporation; UBEPOL®360L and UBEPOL® 150L and UBEPOL-BR rubbers, commercially available fromUBE Industries, Ltd. of Tokyo, Japan; KINEX® 7245 and KINEX® 7265,commercially available from Goodyear of Akron, Ohio; SE BR-1220, andTAKTENE® 1203G1, 220, and 221, commercially available from Dow ChemicalCompany; Europrene® NEOCIS® BR 40 and BR 60, commercially available fromPolimeri Europa; and BR 01, BR 730, BR 735, BR 11, and BR 51,commercially available from Japan Synthetic Rubber Co., Ltd; PETROFLEX®BRNd-40; and KARBOCHEM® ND40, ND45, and ND60, commercially availablefrom Karbochem.

The base rubber may also comprise high or medium Mooney viscosityrubber, or blends thereof. A “Mooney” unit is a unit used to measure theplasticity of raw or unvulcanized rubber. The plasticity in a “Mooney”unit is equal to the torque, measured on an arbitrary scale, on a diskin a vessel that contains rubber at a temperature of 100° C. and rotatesat two revolutions per minute. The measurement of Mooney viscosity isdefined according to ASTM D-1646.

The Mooney viscosity range is preferably greater than about 40, morepreferably in the range from about 40 to about 80 and more preferably inthe range from about 40 to about 60. Polybutadiene rubber with higherMooney viscosity may also be used, so long as the viscosity of thepolybutadiene does not reach a level where the high viscositypolybutadiene clogs or otherwise adversely interferes with themanufacturing machinery. It is contemplated that polybutadiene withviscosity less than 65 Mooney can be used with the present invention.

In one embodiment of the present invention, golf ball cores made withmid- to high-Mooney viscosity polybutadiene material exhibit increasedresiliency (and, therefore, distance) without increasing the hardness ofthe ball. Such cores are soft, i.e., compression less than about 60 andmore specifically in the range of about 50-55. Cores with compression inthe range of from about 30 about 50 are also within the range of thispreferred embodiment.

Commercial sources of suitable mid- to high-Mooney viscositypolybutadiene include Bayer AG CB23 (Nd-catalyzed), which has a Mooneyviscosity of around 50 and is a highly linear polybutadiene, and Shell1220 (Co-catalyzed). If desired, the polybutadiene can also be mixedwith other elastomers known in the art, such as other polybutadienerubbers, natural rubber, styrene butadiene rubber, and/or isoprenerubber in order to further modify the properties of the core. When amixture of elastomers is used, the amounts of other constituents in thecore composition are typically based on 100 parts by weight of the totalelastomer mixture.

In one preferred embodiment, the base rubber comprises a Nd-catalyzedpolybutadiene, a rare earth-catalyzed polybutadiene rubber, or blendsthereof. If desired, the polybutadiene can also be mixed with otherelastomers known in the art such as natural rubber, polyisoprene rubberand/or styrene-butadiene rubber in order to modify the properties of thecore. Other suitable base rubbers include thermosetting materials suchas, ethylene propylene diene monomer rubber, ethylene propylene rubber,butyl rubber, halobutyl rubber, hydrogenated nitrile butadiene rubber,nitrile rubber, and silicone rubber.

Thermoplastic elastomers (TPE) many also be used to modify theproperties of the core layers, or the uncured core layer stock byblending with the base thermoset rubber. These TPEs include natural orsynthetic balata, or high trans-polyisoprene, high trans-polybutadiene,or any styrenic block copolymer, such as styrene ethylene butadienestyrene, styrene-isoprene-styrene, etc., a metallocene or othersingle-site catalyzed polyolefin such as ethylene-octene, orethylene-butene, or thermoplastic polyurethanes (TPU), includingcopolymers, e.g. with silicone. Other suitable TPEs for blending withthe thermoset rubbers of the present invention include PEBAX®, which isbelieved to comprise polyether amide copolymers, HYTREL®, which isbelieved to comprise polyether ester copolymers, thermoplastic urethane,and KRATON®, which is believed to comprise styrenic block copolymerselastomers. Any of the TPEs or TPUs above may also contain functionalitysuitable for grafting, including maleic acid or maleic anhydride.

Additional polymers may also optionally be incorporated into the baserubber. Examples include, but are not limited to, thermoset elastomerssuch as core regrind, thermoplastic vulcanizate, copolymeric ionomer,terpolymeric ionomer, polycarbonate, polyamide, copolymeric polyamide,polyesters, polyvinyl alcohols, acrylonitrile-butadiene-styrenecopolymers, polyarylate, polyacrylate, polyphenylene ether,impact-modified polyphenylene ether, high impact polystyrene, diallylphthalate polymer, styrene-acrylonitrile polymer (SAN) (includingolefin-modified SAN and acrylonitrile-styrene-acrylonitrile polymer),styrene-maleic anhydride copolymer, styrenic copolymer, functionalizedstyrenic copolymer, functionalized styrenic terpolymer, styrenicterpolymer, cellulose polymer, liquid crystal polymer, ethylene-vinylacetate copolymers, polyurea, and polysiloxane or anymetallocene-catalyzed polymers of these species.

Suitable polyamides for use as an additional polymeric material incompositions within the scope of the present invention also includeresins obtained by: (1) polycondensation of (a) a dicarboxylic acid,such as oxalic acid, adipic acid, sebacic acid, terephthalic acid,isophthalic acid, or 1,4-cyclohexanedicarboxylic acid, with (b) adiamine, such as ethylenediamine, tetramethylenediamine,pentamethylenediamine, hexamethylenediamine, or decamethylenediamine,1,4-cyclohexanediamine, or m-xylylenediamine; (2) a ring-openingpolymerization of cyclic lactam, such as ε-caprolactam or Ω-laurolactam;(3) polycondensation of an aminocarboxylic acid, such as 6-aminocaproicacid, 9-aminononanoic acid, 11-aminoundecanoic acid, or12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam witha dicarboxylic acid and a diamine. Specific examples of suitablepolyamides include NYLON 6, NYLON 66, NYLON 610, NYLON 11, NYLON 12,copolymerized NYLON, NYLON MXD6, and NYLON 46.

Suitable peroxide initiating agents include dicumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy) hexane;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne;2,5-dimethyl-2,5-di(benzoylperoxy) hexane;2,2′-bis(t-butylperoxy)-di-iso-propylbenzene;1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane; n-butyl4,4-bis(t-butyl-peroxy)valerate; t-butyl perbenzoate; benzoyl peroxide;n-butyl 4,4′-bis(butylperoxy) valerate; di-t-butyl peroxide; or2,5-di-(t-butylperoxy)-2,5-dimethyl hexane, lauryl peroxide, t-butylhydroperoxide, α-α bis(t-butylperoxy) diisopropylbenzene,di(2-t-butyl-peroxyisopropyl)benzene, di-t-amyl peroxide, di-t-butylperoxide. Preferably, the rubber composition includes from about 0.25 toabout 5.0 parts by weight peroxide per 100 parts by weight rubber (phr),more preferably 0.5 phr to 3 phr, most preferably 0.5 phr to 1.5 phr. Ina most preferred embodiment, the peroxide is present in an amount ofabout 0.8 phr. These ranges of peroxide are given assuming the peroxideis 100% active, without accounting for any carrier that might bepresent. Because many commercially available peroxides are sold alongwith a carrier compound, the actual amount of active peroxide presentmust be calculated. Commercially-available peroxide initiating agentsinclude DICUP™ family of dicumyl peroxides (including DICUP™ R, DICUP™40C and DICUP™ 40KE) available from Crompton (Geo Specialty Chemicals).Similar initiating agents are available from AkroChem, Lanxess,Flexsys/Harwick and R. T. Vanderbilt. Another commercially-available andpreferred initiating agent is TRIGONOX™ 265-50B from Akzo Nobel, whichis a mixture of 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane anddi(2-t-butylperoxyisopropyl) benzene. TRIGONOX™ peroxides are generallysold on a carrier compound.

Suitable reactive co-agents include, but are not limited to, metal saltsof diacrylates, dimethacrylates, and monomethacrylates suitable for usein this invention include those wherein the metal is zinc, magnesium,calcium, barium, tin, aluminum, lithium, sodium, potassium, iron,zirconium, and bismuth. Zinc diacrylate (ZDA) is preferred, but thepresent invention is not limited thereto. ZDA provides golf balls with ahigh initial velocity. The ZDA can be of various grades of purity. Forthe purposes of this invention, the lower the quantity of zinc stearatepresent in the ZDA the higher the ZDA purity. ZDA containing less thanabout 10% zinc stearate is preferable. More preferable is ZDA containingabout 4-8% zinc stearate. Suitable, commercially available zincdiacrylates include those from Sartomer Co. The preferred concentrationsof ZDA that can be used are about 10 phr to about 40 phr, morepreferably 20 phr to about 35 phr, most preferably 25 phr to about 35phr. In a particularly preferred embodiment, the reactive co-agent ispresent in an amount of about 29 phr to about 31 phr.

Additional preferred co-agents that may be used alone or in combinationwith those mentioned above include, but are not limited to,trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, andthe like. It is understood by those skilled in the art, that in the casewhere these co-agents may be liquids at room temperature, it may beadvantageous to disperse these compounds on a suitable carrier topromote ease of incorporation in the rubber mixture.

Antioxidants are compounds that inhibit or prevent the oxidativebreakdown of elastomers, and/or inhibit or prevent reactions that arepromoted by oxygen radicals. Some exemplary antioxidants that may beused in the present invention include, but are not limited to, quinolinetype antioxidants, amine type antioxidants, and phenolic typeantioxidants. A preferred antioxidant is2,2′-methylene-bis-(4-methyl-6-t-butylphenol) available as VANOX® MBPCfrom R. T. Vanderbilt. Other polyphenolic antioxidants include VANOX® T,VANOX® L, VANOX® SKT, VANOX® SWP, VANOX® 13 and VANOX® 1290.

Suitable antioxidants include, but are not limited to,alkylene-bis-alkyl substituted cresols, such as4,4′-methylene-bis(2,5-xylenol); 4,4′-ethylidene-bis-(6-ethyl-m-cresol);4,4′-butylidene-bis-(6-t-butyl-m-cresol);4,4′-decylidene-bis-(6-methyl-m-cresol);4,4′-methylene-bis-(2-amyl-m-cresol);4,4′-propylidene-bis-(5-hexyl-m-cresol);3,3′-decylidene-bis-(5-ethyl-p-cresol);2,2′-butylidene-bis-(3-n-hexyl-p-cresol);4,4′-(2-butylidene)-bis-(6-t-butyl-m-cresol);3,3′-4(decylidene)-bis-(5-ethyl-p-cresol);(2,5-dimethyl-4-hydroxyphenyl) (2-hydroxy-3,5-dimethylphenyl) methane;(2-methyl-4-hydroxy-5-ethylphenyl) (2-ethyl-3-hydroxy-5-methylphenyl)methane; (3-methyl-5-hydroxy-6-t-butylphenyl)(2-hydroxy-4-methyl-5-decylphenyl)-n-butyl methane;(2-hydroxy-4-ethyl-5-methylphenyl)(2-decyl-3-hydroxy-4-methylphenyl)butylamylmethane;(3-ethyl-4-methyl-5-hydroxyphenyl)-(2,3-dimethyl-3-hydroxy-phenyl)nonylmethane;(3-methyl-2-hydroxy-6-ethylphenyl)-(2-isopropyl-3-hydroxy-5-methyl-phenyl)cyclohexylmethane;(2-methyl-4-hydroxy-5-methylphenyl)(2-hydroxy-3-methyl-5-ethylphenyl)dicyclohexyl methane; and the like.

Other suitable antioxidants include, but are not limited to, substitutedphenols, such as 2-tert-butyl-4-methoxyphenol;3-tert-butyl-4-methoxyphenol; 3-tert-octyl-4-methoxyphenol;2-methyl-4-methoxyphenol; 2-stearyl-4-n-butoxyphenol;3-t-butyl-4-stearyloxyphenol; 3-lauryl-4-ethoxyphenol;2,5-di-t-butyl-4-methoxyphenol; 2-methyl-4-methoxyphenol;2-(1-methycyclohexyl)-4-methoxyphenol; 2-t-butyl-4-dodecyloxyphenol;2-(1-methylbenzyl)-4-methoxyphenol; 2-t-octyl-4-methoxyphenol; methylgallate; n-propyl gallate; n-butyl gallate; lauryl gallate; myristylgallate; stearyl gallate; 2,4,5-trihydroxyacetophenone;2,4,5-trihydroxy-n-butyrophenone; 2,4,5-trihydroxystearophenone;2,6-ditert-butyl-4-methylphenol; 2,6-ditert-octyl-4-methylphenol;2,6-ditert-butyl-4-stearylphenol; 2-methyl-4-methyl-6-tert-butylphenol;2,6-distearyl-4-methylphenol; 2,6-dilauryl-4-methylphenol;2,6-di(n-octyl)-4-methylphenol; 2,6-di(n-hexadecyl)-4-methylphenol;2,6-di(1-methylundecyl)-4-methylphenol;2,6-di(1-methylheptadecyl)-4-methylphenol;2,6-di(trimethylhexyl)-4-methylphenol;2,6-di(1,1,3,3-tetramethyloctyl)-4-methylphenol; 2-n-dodecyl-6-tertbutyl-4-methylphenol; 2-n-dodecyl-6-(1-methylundecyl)-4-methylphenol;2-n-dodecyl-6-(1,1,3,3-tetramethyloctyl)-4-methylphenol;2-n-dodecyl-6-n-octadecyl-4-methylphenol;2-n-dodecyl-6-n-octyl-4-methylphenol;2-methyl-6-n-octadecyl-4-methylphenol;2-n-dodecyl-6-(1-methylheptadecyl)-4-methylphenol;2,6-di(1-methylbenzyl)-4-methylphenol;2,6-di(1-methylcyclohexyl)-4-methylphenol;2,6-(1-methylcyclohexyl)-4-methylphenol;2-(1-methylbenzyl)-4-methylphenol; and related substituted phenols.

More suitable antioxidants include, but are not limited to, alkylenebisphenols, such as 4,4′-butylidene bis(3-methyl-6-t-butyl phenol);2,2-butylidene bis (4,6-dimethyl phenol); 2,2′-butylidenebis(4-methyl-6-t-butyl phenol); 2,2′-butylidene bis(4-t-butyl-6-methylphenol); 2,2′-ethylidene bis(4-methyl-6-t-butylphenol); 2,2′-methylenebis(4,6-dimethyl phenol); 2,2′-methylene bis(4-methyl-6-t-butyl phenol);2,2′-methylene bis(4-ethyl-6-t-butyl phenol); 4,4′-methylenebis(2,6-di-t-butyl phenol); 4,4′-methylene bis(2-methyl-6-t-butylphenol); 4,4′-methylene bis(2,6-dimethyl phenol); 2,2′-methylenebis(4-t-butyl-6-phenyl phenol);2,2′-dihydroxy-3,3′,5,5′-tetramethylstilbene; 2,2′-isopropylidenebis(4-methyl-6-t-butyl phenol); ethylene bis (beta-naphthol);1,5-dihydroxy naphthalene; 2,2′-ethylene bis (4-methyl-6-propyl phenol);4,4′-methylene bis(2-propyl-6-t-butyl phenol); 4,4′-ethylene bis(2-methyl-6-propyl phenol); 2,2′-methylene bis(5-methyl-6-t-butylphenol); and 4,4′-butylidene bis(6-t-butyl-3-methyl phenol).

Suitable antioxidants further include, but are not limited to, alkylenetrisphenols, such as 2,6-bis (2′-hydroxy-3′-t-butyl-5′-methylbenzyl)-4-methyl phenol; 2,6-bis (2′-hydroxy-3′-t-ethyl-5′-butylbenzyl)-4-methyl phenol; and 2,6-bis(2′-hydroxy-3′-t-butyl-5′-propylbenzyl)-4-methyl phenol.

The antioxidant is typically present in an amount of about 0.1 phr toabout 5 phr, preferably from about 0.1 phr to about 2 phr, morepreferably about 0.1 phr to about 1 phr. In a particularly preferredembodiment, the antioxidant is present in an amount of about 0.4 phr.

In an alternative embodiment, the antioxidant should be present in anamount to ensure that the hardness gradient of the inventive cores isnegative. Preferably, about 0.2 phr to about 1 phr antioxidant is addedto the core layer (inner core or outer core layer) formulation, morepreferably, about 0.3 to about 0.8 phr, and most preferably 0.4 to about0.7 phr. Preferably, about 0.25 phr to about 1.5 phr of peroxide ascalculated at 100% active can be added to the core formulation, morepreferably about 0.5 phr to about 1.2 phr, and most preferably about 0.7phr to about 1.0 phr. The ZDA amount can be varied to suit the desiredcompression, spin and feel of the resulting golf ball. The cure regimecan have a temperature range between from about 290° F. to about 335°F., more preferably about 300° F. to about 325° F., and the stock isheld at that temperature for at least about 10 minutes to about 30minutes.

The thermoset rubber composition of the present invention may alsoinclude an optional soft and fast agent. As used herein, “soft and fastagent” means any compound or a blend thereof that that is capable ofmaking a core 1) be softer (lower compression) at constant COR or 2)have a higher COR at equal compression, or any combination thereof, whencompared to a core equivalently prepared without a soft and fast agent.Preferably, the composition of the present invention contains from about0.05 phr to about 10.0 phr soft and fast agent. In one embodiment, thesoft and fast agent is present in an amount of about 0.05 phr to about3.0 phr, preferably about 0.05 phr to about 2.0 phr, more preferablyabout 0.05 phr to about 1.0 phr. In another embodiment, the soft andfast agent is present in an amount of about 2.0 phr to about 5.0 phr,preferably about 2.35 phr to about 4.0 phr, and more preferably about2.35 phr to about 3.0 phr. In an alternative high concentrationembodiment, the soft and fast agent is present in an amount of about 5.0phr to about 10.0 phr, more preferably about 6.0 phr to about 9.0 phr,most preferably about 7.0 phr to about 8.0 phr. In a most preferredembodiment, the soft and fast agent is present in an amount of about 2.6phr.

Suitable soft and fast agents include, but are not limited to,organosulfur or metal-containing organosulfur compounds, an organicsulfur compound, including mono, di, and polysulfides, a thiol, ormercapto compound, an inorganic sulfide compound, a Group VIA compound,or mixtures thereof. The soft and fast agent component may also be ablend of an organosulfur compound and an inorganic sulfide compound.

Suitable soft and fast agents of the present invention include, but arenot limited to those having the following general formula:

where R₁-R₅ can be C₁-C₈ alkyl groups; halogen groups; thiol groups(—SH), carboxylated groups; sulfonated groups; and hydrogen; in anyorder; and also pentafluorothiophenol; 2-fluorothiophenol;3-fluorothiophenol; 4-fluorothiophenol; 2,3-fluorothiophenol;2,4-fluorothiophenol; 3,4-fluorothiophenol; 3,5-fluorothiophenol2,3,4-fluorothiophenol; 3,4,5-fluorothiophenol;2,3,4,5-tetrafluorothiophenol; 2,3,5,6-tetrafluorothiophenol;4-chlorotetrafluorothiophenol; pentachlorothiophenol;2-chlorothiophenol; 3-chlorothiophenol; 4-chlorothiophenol;2,3-chlorothiophenol; 2,4-chlorothiophenol; 3,4-chlorothiophenol;3,5-chlorothiophenol; 2,3,4-chlorothiophenol; 3,4,5-chlorothiophenol;2,3,4,5-tetrachlorothiophenol; 2,3,5,6-tetrachlorothiophenol;pentabromothiophenol; 2-bromothiophenol; 3-bromothiophenol;4-bromothiophenol; 2,3-bromothiophenol; 2,4-bromothiophenol;3,4-bromothiophenol; 3,5-bromothiophenol; 2,3,4-bromothiophenol;3,4,5-bromothiophenol; 2,3,4,5-tetrabromothiophenol;2,3,5,6-tetrabromothiophenol; pentaiodothiophenol; 2-iodothiophenol;3-iodothiophenol; 4-iodothiophenol; 2,3-iodothiophenol;2,4-iodothiophenol; 3,4-iodothiophenol; 3,5-iodothiophenol;2,3,4-iodothiophenol; 3,4,5-iodothiophenol; 2,3,4,5-tetraiodothiophenol;2,3,5,6-tetraiodothiophenoland; and their zinc salts. Preferably, thehalogenated thiophenol compound is pentachlorothiophenol, which iscommercially available in neat form or under the tradename STRUKTOL®, aclay-based carrier containing the sulfur compound pentachlorothiophenolloaded at 45 percent (correlating to 2.4 parts PCTP). STRUKTOL® iscommercially available from Struktol Company of America of Stow, Ohio.PCTP is commercially available in neat form from eChinachem of SanFrancisco, Calif. and in the salt form from eChinachem of San Francisco,Calif. Most preferably, the halogenated thiophenol compound is the zincsalt of pentachlorothiophenol, which is commercially available fromeChinachem of San Francisco, Calif.

As used herein when referring to the invention, the term “organosulfurcompound(s)” refers to any compound containing carbon, hydrogen, andsulfur, where the sulfur is directly bonded to at least 1 carbon. Asused herein, the term “sulfur compound” means a compound that iselemental sulfur, polymeric sulfur, or a combination thereof. It shouldbe further understood that the term “elemental sulfur” refers to thering structure of S₈ and that “polymeric sulfur” is a structureincluding at least one additional sulfur relative to elemental sulfur.

Additional suitable examples of soft and fast agents (that are alsobelieved to be cis-to-trans catalysts) include, but are not limited to,4,4′-diphenyl disulfide; 4,4′-ditolyl disulfide; 2,2′-benzamido diphenyldisulfide; bis(2-aminophenyl) disulfide; bis(4-aminophenyl) disulfide;bis(3-aminophenyl) disulfide; 2,2′-bis(4-aminonaphthyl) disulfide;2,2′-bis(3-aminonaphthyl) disulfide; 2,2′-bis(4-aminonaphthyl)disulfide; 2,2′-bis(5-aminonaphthyl) disulfide;2,2′-bis(6-aminonaphthyl) disulfide; 2,2′-bis(7-aminonaphthyl)disulfide; 2,2′-bis(8-aminonaphthyl) disulfide;1,1′-bis(2-aminonaphthyl) disulfide; 1,1′-bis(3-aminonaphthyl)disulfide; 1,1′-bis(3-aminonaphthyl) disulfide;1,1′-bis(4-aminonaphthyl) disulfide; 1,1′-bis(5-aminonaphthyl)disulfide; 1,1′-bis(6-aminonaphthyl) disulfide;1,1′-bis(7-aminonaphthyl) disulfide; 1,1′-bis(8-aminonaphthyl)disulfide; 1,2′-diamino- 1,2′-dithiodinaphthalene;2,3′-diamino-1,2′-dithiodinaphthalene; bis(4-chlorophenyl) disulfide;bis(2-chlorophenyl) disulfide; bis(3-chlorophenyl) disulfide;bis(4-bromophenyl) disulfide; bis(2-bromophenyl) disulfide;bis(3-bromophenyl) disulfide; bis(4-fluorophenyl) disulfide;bis(4-iodophenyl) disulfide; bis(2,5-dichlorophenyl) disulfide;bis(3,5-dichlorophenyl) disulfide; bis (2,4-dichlorophenyl) disulfide;bis(2,6-dichlorophenyl) disulfide; bis(2,5-dibromophenyl) disulfide;bis(3,5-dibromophenyl) disulfide; bis(2-chloro-5-bromophenyl) disulfide;bis(2,4,6-trichlorophenyl) disulfide; bis(2,3,4,5,6-pentachlorophenyl)disulfide; bis(4-cyanophenyl) disulfide; bis(2-cyanophenyl) disulfide;bis(4-nitrophenyl) disulfide; bis(2-nitrophenyl) disulfide;2,2′-dithiobenzoic acid ethylester; 2,2′-dithiobenzoic acid methylester;2,2′-dithiobenzoic acid; 4,4′-dithiobenzoic acid ethylester;bis(4-acetylphenyl) disulfide; bis(2-acetylphenyl) disulfide;bis(4-formylphenyl) disulfide; bis(4-carbamoylphenyl) disulfide;1,1′-dinaphthyl disulfide; 2,2′-dinaphthyl disulfide; 1,2′-dinaphthyldisulfide; 2,2′-bis(l -chlorodinaphthyl) disulfide;2,2′-bis(1-bromonaphthyl) disulfide; 1,1′-bis(2-chloronaphthyl)disulfide; 2,2′-bis(1-cyanonaphthyl) disulfide;2,2′-bis(1-acetylnaphthyl) disulfide; and the like; or a mixturethereof. Preferred organosulfur components include 4,4′-diphenyldisulfide, 4,4′-ditolyl disulfide, or 2,2′-benzamido diphenyl disulfide,or a mixture thereof. A more preferred organosulfur component includes4,4′-ditolyl disulfide. In another embodiment, metal-containingorganosulfur components can be used according to the invention. Suitablemetal-containing organosulfur components include, but are not limitedto, cadmium, copper, lead, and tellurium analogs ofdiethyldithiocarbamate, diamyldithiocarbamate, anddimethyldithiocarbamate, or mixtures thereof.

Suitable substituted or unsubstituted aromatic organic components thatdo not include sulfur or a metal include, but are not limited to,4,4′-diphenyl acetylene, azobenzene, or a mixture thereof. The aromaticorganic group preferably ranges in size from C₆ to C₂₀, and morepreferably from C₆ to C₁₀. Suitable inorganic sulfide componentsinclude, but are not limited to titanium sulfide, manganese sulfide, andsulfide analogs of iron, calcium, cobalt, molybdenum, tungsten, copper,selenium, yttrium, zinc, tin, and bismuth.

A substituted or unsubstituted aromatic organic compound is alsosuitable as a soft and fast agent. Suitable substituted or unsubstitutedaromatic organic components include, but are not limited to, componentshaving the formula (R₁)_(x)-R₃-M-R₄-(R₂)_(y), wherein R₁ and R₂ are eachhydrogen or a substituted or unsubstituted C₁₋₂₀ linear, branched, orcyclic alkyl, alkoxy, or alkylthio group, or a single, multiple, orfused ring C₆ to C₂₄ aromatic group; x and y are each an integer from 0to 5; R₃ and R₄ are each selected from a single, multiple, or fused ringC₆ to C₂₄ aromatic group; and M includes an azo group or a metalcomponent. R₃ and R₄ are each preferably selected from a C₆ to C₁oaromatic group, more preferably selected from phenyl, benzyl, naphthyl,benzamido, and benzothiazyl. R₁ and R₂ are each preferably selected froma substituted or unsubstituted C₁₋₁₀ linear, branched, or cyclic alkyl,alkoxy, or alkylthio group or a C₆ to C₁O aromatic group. When R₁, R₂,R₃, or R₄, are substituted, the substitution may include one or more ofthe following substituent groups: hydroxy and metal salts thereof;mercapto and metal salts thereof; halogen; amino, nitro, cyano, andamido; carboxyl including esters, acids, and metal salts thereof, silyl;acrylates and metal salts thereof; sulfonyl or sulfonamide; andphosphates and phosphites. When M is a metal component, it may be anysuitable elemental metal available to those of ordinary skill in theart. Typically, the metal will be a transition metal, althoughpreferably it is tellurium or selenium. In one embodiment, the aromaticorganic compound is substantially free of metal, while in anotherembodiment the aromatic organic compound is completely free of metal.

The soft and fast agent can also include a Group VIA component.Elemental sulfur and polymeric sulfur are commercially available fromElastochem, Inc. of Chardon, Ohio. Exemplary sulfur catalyst compoundsinclude PB(RM-S)-80 elemental sulfur and PB(CRST)-65 polymeric sulfur,each of which is available from Elastochem, Inc. An exemplary telluriumcatalyst under the tradename TELLOY® and an exemplary selenium catalystunder the tradename VANDEX® are each commercially available from RTVanderbilt.

Other suitable soft and fast agents include, but are not limited to,hydroquinones, benzoquinones, quinhydrones, catechols, and resorcinols.

Suitable hydroquinone compounds include compounds represented by thefollowing formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are hydrogen; halogen; alkyl; carboxyl;metal salts thereof, and esters thereof, acetate and esters thereof;formyl; acyl; acetyl; halogenated carbonyl; sulfo and esters thereof;halogenated sulfonyl; sulfino; alkylsulfinyl; carbamoyl; halogenatedalkyl; cyano; alkoxy; hydroxy and metal salts thereof; amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Other suitable hydroquinone compounds include, but are not limited to,hydroquionone; tetrachlorohydroquinone; 2-chlorohydroquionone;2-bromohydroquinone; 2,5-dichlorohydroquinone; 2,5-dibromohydroquinone;tetrabromohydroquinone; 2-methylhydroquinone; 2-t-butylhydroquinone;2,5-di-t-amylhydroquinone; and 2-(2-chlorophenyl) hydroquinone hydrate.

More suitable hydroquinone compounds include compounds represented bythe following formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are a metal salt of a carboxyl; acetateand esters thereof, hydroxy; a metal salt of a hydroxy; amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Suitable benzoquinone compounds include compounds represented by thefollowing formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are hydrogen; halogen; alkyl; carboxyl;metal salts thereof, and esters thereof; acetate and esters thereof;formyl; acyl; acetyl; halogenated carbonyl; sulfo and esters thereof;halogenated sulfonyl; sulfino; alkylsulfinyl; carbamoyl; halogenatedalkyl; cyano; alkoxy; hydroxy and metal salts thereof, amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Other suitable benzoquinone compounds include one or more compoundsrepresented by the following formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are a metal salt of a carboxyl; acetateand esters thereof, hydroxy; a metal salt of a hydroxy; amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Suitable quinhydrones include one or more compounds represented by thefollowing formula, and hydrates thereof:

wherein each R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ are hydrogen; halogen;alkyl; carboxyl; metal salts thereof, and esters thereof; acetate andesters thereof; formyl; acyl; acetyl; halogenated carbonyl; sulfo andesters thereof; halogenated sulfonyl; sulfino; alkylsulfinyl; carbamoyl;halogenated alkyl; cyano; alkoxy; hydroxy and metal salts thereof;amino; nitro; aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Other suitable quinhydrones include those having the above formula,wherein each R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ are a metal salt of acarboxyl; acetate and esters thereof; hydroxy; a metal salt of ahydroxy; amino; nitro; aryl; aryloxy; arylalkyl; nitroso; acetamido; orvinyl.

Suitable catechols include one or more compounds represented by thefollowing formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are hydrogen; halogen; alkyl; carboxyl;metal salts thereof, and esters thereof; acetate and esters thereof;formyl; acyl; acetyl; halogenated carbonyl; sulfo and esters thereof;halogenated sulfonyl; sulfino; alkylsulfinyl; carbamoyl; halogenatedalkyl; cyano; alkoxy; hydroxy and metal salts thereof; amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Suitable resorcinols include one or more compounds represented by thefollowing formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are hydrogen; halogen; alkyl; carboxyl;metal salts thereof, and esters thereof; acetate and esters thereof;formyl; acyl; acetyl; halogenated carbonyl; sulfo and esters thereof;halogenated sulfonyl; sulfino; alkylsulfinyl; carbamoyl; halogenatedalkyl; cyano; alkoxy; hydroxy and metal salts thereof; amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Fillers may also be added to the thermoset rubber composition of thecore to adjust the density of the composition, up or down. Typically,fillers include materials such as tungsten, zinc oxide, barium sulfate,silica, calcium carbonate, zinc carbonate, metals, metal oxides andsalts, regrind (recycled core material typically ground to about 30 meshparticle), high-Mooney-viscosity rubber regrind, trans-regrind corematerial (recycled core material containing high trans-isomer ofpolybutadiene), and the like. When trans-regrind is present, the amountof trans-isomer is preferably between about 10% and about 60%. In apreferred embodiment of the invention, the core comprises polybutadienehaving a cis-isomer content of greater than about 95% and trans-regrindcore material (already vulcanized) as a filler. Any particle sizetrans-regrind core material is sufficient, but is preferably less thanabout 125 μm.

Fillers added to one or more portions of the golf ball typically includeprocessing aids or compounds to affect rheological and mixingproperties, density-modifying fillers, tear strength, or reinforcementfillers, and the like. The fillers are generally inorganic, and suitablefillers include numerous metals or metal oxides, such as zinc oxide andtin oxide, as well as barium sulfate, zinc sulfate, calcium carbonate,barium carbonate, clay, tungsten, tungsten carbide, an array of silicas,and mixtures thereof. Fillers may also include various foaming agents orblowing agents which may be readily selected by one of ordinary skill inthe art. Fillers may include polymeric, ceramic, metal, and glassmicrospheres may be solid or hollow, and filled or unfilled. Fillers aretypically also added to one or more portions of the golf ball to modifythe density thereof to conform to uniform golf ball standards. Fillersmay also be used to modify the weight of the center or at least oneadditional layer for specialty balls, e.g., a lower weight ball ispreferred for a player having a low swing speed.

Materials such as tungsten, zinc oxide, barium sulfate, silica, calciumcarbonate, zinc carbonate, metals, metal oxides and salts, and regrind(recycled core material typically ground to about 30 mesh particle) arealso suitable fillers.

The polybutadiene and/or any other base rubber or elastomer system mayalso be foamed, or filled with hollow microspheres or with expandablemicrospheres which expand at a set temperature during the curing processto any low specific gravity level. Other ingredients such as sulfuraccelerators, e.g., tetra methylthiuram di, tri, or tetrasulfide, and/ormetal-containing organosulfur components may also be used according tothe invention. Suitable metal-containing containing organosulfuraccelerators include, but are not limited to, cadmium, copper, lead, andtellurium analogs of diethyldithiocarbamate, diamyldithiocarbamate, anddimethyldithiocarbamate, or mixtures thereof. Other ingredients such asprocessing aids e.g., fatty acids and/or their metal salts, processingoils, dyes and pigments, as well as other additives known to one skilledin the art may also be used in the present invention in amountssufficient to achieve the purpose for which they are typically used.

A number of cores were formed based on the formulation and cure cycledescribed in TABLE I below and core hardness values are reported inTABLE II below.

TABLE I Formulation (phr) Ex 1 Ex 2 Ex 3 Comp Ex 1 Comp Ex 2 Comp Ex 3SR-526⁺ 34.0 34.0 31.2 29.0 29.0 29.0 ZnO 5 5 5 5 5 5 BaSO₄ 11.2 11.216.1 13.8 13.8 13.8 Vanox MBPC* 0.40 0.40 0.40 — 0.50 —Trigonox-265-50B** 1.4 1.4 1.6 — — 0.8 Perkadox BC-FF*** — — — 1.0 1.6 —polybutadiene 100 100 100 100 100 100 ZnPCTP 2.35 2.35 2.60 2.35 2.352.35 regrind — — 17 17 — — antioxidant/initiator ratio 0.57 0.57 0.50 —0.31 — Cure Temp. (° F.) 305 315 320 350 335 335 Cure Time (min) 14 1116 11 11 11 Properties diameter (in) 1.530 1.530 1.530 1.530 1.530 1.530compression 69 63 70 69 47 — COR @ 125 ft/s 0.808 0.806 0.804 0.804 — —*Vanox MBPC: 2,2′-methylene-bis-(4-methyl-6-t-butylphenol) availablefrom R. T. Vanderbilt Company Inc.; **Trigonox 265-50B: a mixture of1,1-di(t-butylperoxy)-3,3,5-trimethycyclohexane anddi(2-t-butylperoxyisopropyl)benzene 50% active on an inert carrieravailable from Akzo Nobel; ***Perkadox BC-FF: Dicumyl peroxide (99%-100%active) available from Akzo Nobel; and ⁺ SR-526: ZDA available fromSartomer

TABLE II Shore C Hardness Distance Comp Comp Comp from Center Ex 1 Ex 2Ex 3 Ex 1 Ex 2 Ex 3 Center 73 70 71 61 52 61  2 74 71 72 67 57 62  4 7472 73 70 62 65  6 75 73 73 72 64 67  8 75 73 73 73 64 69 10 75 73 74 7364 71 12 74 74 73 72 66 72 14 74 74 72 73 70 73 16 70 71 70 77 71 73 1860 60 63 80 72 73 Surface 63 70 66 85 73 74 Surface − −10 0 −5 24 21 13Center

The surface hardness of a core is obtained from the average of a numberof measurements taken from opposing hemispheres of a core, taking careto avoid making measurements on the parting line of the core or onsurface defects, such as holes or protrusions. Hardness measurements aremade pursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plasticby Means of a Durometer.” Because of the curved surface of a core, caremust be taken to insure that the core is centered under the durometerindentor before a surface hardness reading is obtained. A calibrated,digital durometer, capable of reading to 0.1 hardness units is used forall hardness measurements and is set to take hardness readings at 1second after the maximum reading is obtained. The digital durometer mustbe attached to, and its foot made parallel to, the base of an automaticstand, such that the weight on the durometer and attack rate conform toASTM D-2240.

To prepare a core for hardness gradient measurements, the core is gentlypressed into a hemispherical holder having an internal diameterapproximately slightly smaller than the diameter of the core, such thatthe core is held in place in the hemispherical portion of the holderwhile concurrently leaving the geometric central plane of the coreexposed. The core is secured in the holder by friction, such that itwill not move during the cutting and grinding steps, but the friction isnot so excessive that distortion of the natural shape of the core wouldresult. The core is secured such that the parting line of the core isroughly parallel to the top of the holder. The diameter of the core ismeasured 90 degrees to this orientation prior to securing. A measurementis also made from the bottom of the holder to the top of the core toprovide a reference point for future calculations. A rough cut, madeslightly above the exposed geometric center of the core using a band sawor other appropriate cutting tool, making sure that the core does notmove in the holder during this step. The remainder of the core, still inthe holder, is secured to the base plate of a surface grinding machine.The exposed ‘rough’ core surface is ground to a smooth, flat surface,revealing the geometric center of the core, which can be verified bymeasuring the height of the bottom of the holder to the exposed surfaceof the core, making sure that exactly half of the original height of thecore, as measured above, has been removed to within ±0.004 inches.

Leaving the core in the holder, the center of the core is found with acenter square and carefully marked and the hardness is measured at thecenter mark. Hardness measurements at any distance from the center ofthe core may be measured by drawing a line radially outward from thecenter mark, and measuring and marking the distance from the center,typically in 2-mm increments. All hardness measurements performed on theplane passing through the geometric center are performed while the coreis still in the holder and without having disturbed its orientation,such that the test surface is constantly parallel to the bottom of theholder. The hardness difference from any predetermined location on thecore is calculated as the average surface hardness minus the hardness atthe appropriate reference point, e.g., at the center of the core forsingle, solid core, such that a core surface softer than its center willhave a negative hardness gradient.

Referring to TABLES I and II, in Example 1, the surface is 10 Shore Cpoints lower than the center hardness and 12 Shore C points lower thanthe hardest point in the core. In Example 3, the surface is 5 Shore Cpoints lower than the center hardness and 8 Shore C points lower thanthe hardest point in the core. In Example 2, the center and surfacehardness values are equal and the softest point in the core is 10 ShoreC points lower than the surface.

In the examples of the invention presented in TABLE I, the curetemperatures are varied from 305° F. to 320° F. and cure times arevaried from 11 to 16 minutes. The core compositions of examples 1 and 2are identical, and only the cure cycle is changed. In example 3 theamount of antioxidant is identical to examples 1 and 2, but otheringredients are varied as well the cure cycle. Additionally, the ratioof antioxidant to initiator varies from 0.50 to 0.57 from example 1 and2 to example 3.

The ratio of antioxidant to initiator is one factor to control thesurface hardness of the cores. The data shown in TABLE II shows thathardness gradient is at least, but not limited to, a function of theamount of antioxidant and peroxide, their ratio, and the cure cycle. Itshould be noted that higher antioxidant also requires higher peroxideinitiator to maintain the desired compression.

The core of Comparative Example 1, whose composition is shown in TABLE Iwas cured using a conventional cure cycle, with a cure temperature of350° F. and a cure time of 11 minutes. The inventive cores were producedusing cure cycles of 305° F. for 14 minutes, 315° F. for 11 minutes and320° F. for 16 minutes. The hardness gradients of these cores weremeasured and the following observations can be made. For the cores ofthe Comparative Examples, as expected, a conventional hard surface tosoft center gradient can be clearly seen. The gradients for inventivecores follow substantially the same shape as one another.

In all preferred embodiments of invention, the hardness of the core atthe surface is at most about the same as or substantially less than thehardness of the core at the center. Furthermore, the center hardness ofthe core may not be the hardest point in the core, but in all cases, itis preferred that it is at least equal to or harder than the surface.Additionally, the lowest hardness anywhere in the core does not have tooccur at the surface. In some embodiments, the lowest hardness valueoccurs within about the outer 6 mm of the core surface. However, thelowest hardness value within the core can occur at any point from thesurface, up to, but not including the center, as long as the surfacehardness is still equal to, or less than the hardness of the center. Itshould be noted that in the present invention the formulation is thesame throughout the core, or core layer, and no surface treatment isapplied to the core to obtain the preferred surface hardness.

In accordance with another embodiment of the present invention, a golfball is provided with a very low compression core and a thick coverlayer. Preferably, the core for the low compression embodiment has anAtti compression of 30 or less, more preferably 20 or less, mostpreferably 10 or less. While a conventional core (i.e., one having a“positive” hardness gradient) would be sufficient for the lowcompression core embodiment, preferably the core has a zero or, mostpreferably, a “negative” hardness gradient. In this embodiment, the corepreferably has an outer diameter of 1.10 inches to 1.50 inches, morepreferably 1.18 inches to 1.40 inches, and most preferably 1.20 inchesto 1.36 inches. With a very low compression core, it is preferred thatthe cover layer comprise as resilient polymeric material, such as “highacid” ionomers having greater than about 16% by weight acid, such asthose disclosed in U.S. Pat. No. 6,774,189 which is incorporated hereinby reference. The preferred cover layers have a thickness of 0.101inches to 0.250 inches, more preferably 0.125 inches to 0.200 inches,and most preferably 0.14 inches to 0.16 inches.

In a preferred low compression embodiment, the core has a “negative”gradient, a compression of 42 or less, and a COR of 0.750 to 0.790. Thecompression is more preferably about 30 or less. The surface of the corehas a hardness of about 60 Shore C or less, more preferably about 58Shore C or less, most preferably about 55 Shore C orless—correspondingly, the geometric center of the core has a hardnessgreater than the core surface (to define the “negative” hardnessgradient) and about 61 Shore C or less, more preferably about 59 Shore Cor less, most preferably about 56 Shore C or less.

Soft, highly resilient ionomers, are suitable for the cores and layersof the present invention and are preferably formed from the fullneutralization of the acid copolymer(s) of at least one E/X/Y copolymer,where E is ethylene, X is the α,β-ethylenically unsaturated carboxylicacid, and Y is a softening co-monomer. X is preferably present in 2-30(preferably 4-20, most preferably 5-15) wt. % of the polymer, and Y ispreferably present in 17-40 (preferably 20-40, and more preferably24-35) wt. % of the polymer. Preferably, the melt index (MI) of the baseresin is at least 20, or at least 40, more preferably, at least 75 andmost preferably at least 150. Particular soft, resilient ionomersincluded in this invention are partially neutralized ethylene/(meth)acrylic acid/butyl (meth)acrylate copolymers having an MI and level ofneutralization that results in a melt processible polymer that hasuseful physical properties. The copolymers are at least partiallyneutralized. Preferably at least 40, or, more preferably at least 55,even more preferably about 70, and most preferably about 80 of the acidmoiety of the acid copolymer is neutralized by one or more alkali metal,transition metal, or alkaline earth metal cations. Cations useful inmaking the ionomers of this invention comprise lithium, sodium,potassium, magnesium, calcium, barium, or zinc, or a combination of suchcations.

The invention also relates to a “modified” soft, resilient thermoplasticionomer that comprises a melt blend of (a) the acid copolymers or themelt processiible ionomers made therefrom as described above and (b) oneor more organic acid(s) or salt(s) thereof, wherein greater than 80%,preferably greater than 90% of all the acid of (a) and of (b) isneutralized. Preferably, 100% of all the acid of (a) and (b) isneutralized by a cation source. Preferably, an amount of cation sourcein excess of the amount required to neutralize 100% of the acid in (a)and (b) is used to neutralize the acid in (a) and (b). Blends with fattyacids or fatty acid salts are preferred.

The organic acids or salts thereof are added in an amount sufficient toenhance the resilience of the copolymer. Preferably, the organic acidsor salts thereof are added in an amount sufficient to substantiallyremove remaining ethylene crystallinity of the copolymer.

Preferably, the organic acids or salts are added in an amount of atleast about 5% (weight basis) of the total amount of copolymer andorganic acid(s). More preferably, the organic acids or salts thereof areadded in an amount of at least about 15%, even more preferably at leastabout 20%. Preferably, the organic acid(s) are added in an amount up toabout 50% (weight basis) based on the total amount of copolymer andorganic acid. More preferably, the organic acids or salts thereof areadded in an amount of up to about 40%, more preferably, up to about 35%.The non-volatile, non-migratory organic acids preferably are one or morealiphatic, mono-functional organic acids or salts thereof as describedbelow, particularly one or more aliphatic, mono-functional, saturated orunsaturated organic acids having less than 36 carbon atoms or salts ofthe organic acids, preferably stearic acid or oleic acid. Fatty acids orfatty acid salts are most preferred.

Processes for fatty acid (salt) modifications are known in the art.Particularly, the modified highly-neutralized soft, resilient acidcopolymer ionomers of this invention can be produced by:

(a) melt-blending (1) ethylene, α,β-ethylenically unsaturated C₃₋₈carboxylic acid copolymer(s) or melt-processible ionomer(s) thereof thathave their crystallinity disrupted by addition of a softening monomer orother means with (2) sufficient non-volatile, non-migratory organicacids to substantially enhance the resilience and to disrupt (preferablyremove) the remaining ethylene crystallinity, and then concurrently orsubsequently

(b) Adding a sufficient amount of a cation source to increase the levelof neutralization of all the acid moieties (including those in the acidcopolymer and in the organic acid if the non-volatile, non-migratoryorganic acid is an organic acid) to the desired level.

The weight ratio of X to Y in the composition is at least about 1:20.Preferably, the weight ratio of X to Y is at least about 1:15, morepreferably, at least about 1:10. Furthermore, the weight ratio of X to Yis up to about 1:1.67, more preferably up to about 1:2. Most preferably,the weight ratio of X to Y in the composition is up to about 1:2.2.

The acid copolymers used in the present invention to make the ionomersare preferably ‘direct’ acid copolymers (containing high levels ofsoftening monomers). As noted above, the copolymers are at leastpartially neutralized, preferably at least about 40% of X in thecomposition is neutralized. More preferably, at least about 55% of X isneutralized. Even more preferably, at least about 70, and mostpreferably, at least about 80% of X is neutralized. In the event thatthe copolymer is highly neutralized (e.g., to at least 45%, preferably50%, 55%, 70%, or 80%, of acid moiety), the MI of the acid copolymershould be sufficiently high so that the resulting neutralized resin hasa measurable MI in accord with ASTM D-1238, condition E, at 190° C.,using a 2160 gram weight. Preferably this resulting MI will be at least0.1, preferably at least 0.5, and more preferably 1.0 or greater.Preferably, for highly neutralized acid copolymer, the MI of the acidcopolymer base resin is at least 20, or at least 40, at least 75, andmore preferably at least 150.

The acid copolymers preferably comprise alpha olefin, particularlyethylene, C₃₋₈. α,β-ethylenically unsaturated carboxylic acid,particularly acrylic and methacrylic acid, and softening monomers,selected from alkyl acrylate, and alkyl methacrylate, wherein the alkylgroups have from 1-8 carbon atoms, copolymers. By “softening,” it ismeant that the crystallinity is disrupted (the polymer is made lesscrystalline). While the alpha olefin can be a C₂-C₄ alpha olefin,ethylene is most preferred for use in the present invention.Accordingly, it is described and illustrated herein in terms of ethyleneas the alpha olefin.

The acid copolymers, when the alpha olefin is ethylene, can be describedas E/X/Y copolymers where E is ethylene, X is the α,β-ethylenicallyunsaturated carboxylic acid, and Y is a softening co-monomer X ispreferably present in 2-30 (preferably 4-20, most preferably 5-15) wt. %of the polymer, and Y is preferably present in 17-40 (preferably 20-40,most preferably 24-35) wt. % of the polymer.

The ethylene-acid copolymers with high levels of acid (X) are difficultto prepare in continuous polymerizers because of monomer-polymer phaseseparation. This difficulty can be avoided however by use of “co-solventtechnology” as described in U.S. Pat. No. 5,028,674, or by employingsomewhat higher pressures than those which copolymers with lower acidcan be prepared.

Specific acid-copolymers include ethylene/(meth)acrylic acid/n-butyl(meth)acrylate, ethylene/(meth)acrylic acid/iso-butyl(meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate, andethylene/(meth)acrylic acid/ethyl(meth)acrylate terpolymers.

The organic acids employed are aliphatic, mono-functional (saturated,unsaturated, or multi-unsaturated) organic acids, particularly thosehaving fewer than 36 carbon atoms. Also salts of these organic acids maybe employed. Fatty acids or fatty acid salts are preferred. The saltsmay be any of a wide variety, particularly including the barium,lithium, sodium, zinc, bismuth, potassium, strontium, magnesium orcalcium salts of the organic acids. Particular organic acids useful inthe present invention include caproic acid, caprylic acid, capric acid,lauric acid, stearic acid, behenic acid, erucic acid, oleic acid, andlinoleic acid.

The optional filler component is chosen to impart additional density toblends of the previously described components, the selection beingdependent upon the different parts (e.g., cover, mantle, core, center,intermediate layers in a multilayered core or ball) and the type of golfball desired (e.g., one-piece, two-piece, three-piece or multiple-pieceball), as will be more fully detailed below.

Generally, the filler will be inorganic having a density greater thanabout 4 grams/cubic centimeter (g/cm³), preferably greater than 5 g/cm³,and will be present in amounts between 0 to about 60 wt. % based on thetotal weight of the composition. Examples of useful fillers include zincoxide, barium sulfate, lead silicate and tungsten carbide, as well asthe other well-known fillers used in golf balls. It is preferred thatthe filler materials be non-reactive or almost non-reactive and notstiffen or raise the compression nor reduce the coefficient ofrestitution significantly.

Additional optional additives useful in the practice of the subjectinvention include acid copolymer wax (e.g., Allied wax AC 143 believedto be an ethylene/16-18% acrylic acid copolymer with a number averagemolecular weight of 2,040), which assist in preventing reaction betweenthe filler materials (e.g., ZnO) and the acid moiety in the ethylenecopolymer. Other optional additives include TiO₂, which is used as awhitening agent; optical brighteners; surfactants; processing aids; etc.

Ionomers may be blended with conventional ionomeric copolymers (di-,ter-, etc.) , using well-known techniques, to manipulate productproperties as desired. The blends would still exhibit lower hardness andhigher resilience when compared with blends based on conventionalionomers.

Also, ionomers can be blended with non-ionic thermoplastic resins tomanipulate product properties. The non-ionic thermoplastic resins would,by way of non-limiting illustrative examples, include thermoplasticelastomers, such as polyurethane, poly-ether-ester, poly-amide-ether,polyether-urea, PEBAX(® (a family of block copolymers based onpolyether-block-amide, commercially supplied by Atochem),styrene-butadiene-styrene (SBS) block copolymers,styrene(ethylene-butylene)-styrene block copolymers, etc., poly amide(oligomeric and polymeric), polyesters, polyolefins including PE, PP,E/P copolymers, etc., ethylene copolymers with various comonomers, suchas vinyl acetate, (meth)acrylates, (meth)acrylic acid,epoxy-functionalized monomer, CO, etc., functionalized polymers withmaleic anhydride grafting, epoxidization etc., elastomers, such as EPDM,metallocene catalyzed PE and copolymer, ground up powders of thethermoset elastomers, etc. Such thermoplastic blends comprise about 1%to about 99% by weight of a first thermoplastic and about 99% to about1% by weight of a second thermoplastic.

Additionally, the compositions of U.S. Pat. Nos. 6,953,820 and6,653,382, both of which are incorporated herein in their entirety,discuss compositions having high COR when formed into solid spheres.

The thermoplastic composition of this invention comprises a polymerwhich, when formed into a sphere that is 1.50 to 1.54 inches indiameter, has a coefficient of restitution (COR) when measured by firingthe sphere at an initial velocity of 125 ft/s against a steel platepositioned 3 feet from the point where initial velocity and reboundvelocity are determined and by dividing the rebound velocity from theplate by the initial velocity and an Atti compression of no more than100.

The thermoplastic composition of this invention preferably comprises (a)aliphatic, mono-functional organic acid(s) having fewer than 36 carbonatoms; and (b) ethylene, C₃ to C₈ α,β-ethylenically unsaturatedcarboxylic acid copolymer(s) and ionomer(s) thereof, wherein greaterthan 90%, preferably near 100%, and more preferably 100% of all the acidof (a) and (b) are neutralized.

The thermoplastic composition preferably comprises melt-processible,highly-neutralized (greater than 90%, preferably near 100%, and morepreferably 100%) polymer of (1) ethylene, C₃ to C₈ α,β-ethylenicallyunsaturated carboxylic acid copolymers that have their crystallinitydisrupted by addition of a softening monomer or other means such as highacid levels, and (2) non-volatile, non-migratory agents such as organicacids (or salts) selected for their ability to substantially or totallysuppress any remaining ethylene crystallinity. Agents other than organicacids (or salts) may be used.

It has been found that, by modifying an acid copolymer or ionomer with asufficient amount of specific organic acids (or salts thereof); it ispossible to highly neutralize the acid copolymer without losingprocessibility or properties such as elongation and toughness. Theorganic acids employed in the present invention are aliphatic,mono-functional, saturated or unsaturated organic acids, particularlythose having fewer than 36 carbon atoms, and particularly those that arenon-volatile and non-migratory and exhibit ionic array plasticizing andethylene crystallinity suppression properties.

With the addition of sufficient organic acid, greater than 90%, nearly100%, and preferably 100% of the acid moieties in the acid copolymerfrom which the ionomer is made can be neutralized without losing theprocessibility and properties of elongation and toughness.

The melt-processible, highly-neutralized acid copolymer ionomer can beproduced by the following:

(a) melt-blending (1) ethylene α,β-ethylenically unsaturated C₃₋₈carboxylic acid copolymer(s) or melt-processible ionomer(s) thereof(ionomers that are not neutralized to the level that they have becomeintractable, that is not melt-processible) with (1) one or morealiphatic, mono-functional, saturated or unsaturated organic acidshaving fewer than 36 carbon atoms or salts of the organic acids, andthen concurrently or subsequently (b) adding a sufficient amount of acation source to increase the level of neutralization all the acidmoieties (including those in the acid copolymer and in the organic acid)to greater than 90%, preferably near 100%, more preferably to 100%.

Preferably, highly-neutralized thermoplastics of the invention can bemade by:

(a) melt-blending (1) ethylene, α-β-ethylenically unsaturated C₃₋₈carboxylic acid copolymer(s) or melt-processible ionomer(s) thereof thathave their crystallinity disrupted by addition of a softening monomer orother means with (2) sufficient non-volatile, non-migratory agents tosubstantially remove the remaining ethylene crystallinity, and thenconcurrently or subsequently

(b) adding a sufficient amount of a cation source to increase the levelof neutralization all the acid moieties (including those in the acidcopolymer and in the organic acid if the non-volatile, non-migratoryagent is an organic acid) to greater than 90%, preferably near 100%,more preferably to 100%.

The acid copolymers used in the present invention to make the ionomersare preferably ‘direct’ acid copolymers. They are preferably alphaolefin, particularly ethylene, C₃₋₈ α,β-ethylenically unsaturatedcarboxylic acid, particularly acrylic and methacrylic acid, copolymers.They may optionally contain a third softening monomer. By “softening,”it is meant that the crystallinity is disrupted (the polymer is madeless crystalline). Suitable “softening” co-monomers are monomersselected from alkyl acrylate, and alkyl methacrylate, wherein the alkylgroups have from 1-8 carbon atoms.

The acid copolymers, when the alpha olefin is ethylene, can be describedas E/X/Y copolymers where E is ethylene, X is the α,β-ethylenicallyunsaturated carboxylic acid, and Y is a softening comonomer. X ispreferably present in 3-30 (preferably 4-25, most preferably 5-20) wt. %of the polymer, and Y is preferably present in 0-30 (alternatively 3-25or 10-23) wt. % of the polymer. Spheres were prepared using fullyneutralized ionomers A and B as presented in TABLE III.

TABLE III Cation (% M.I. Sample Resin Type (%) Acid Type (%) neut*)(g/10 min) 1A A(60) Oleic (40) Mg (100) 1.0 2B A(60) Oleic (40) Mg(105)* 0.9 3C B(60) Oleic (40) Mg (100) 0.9 4D B(60) Oleic (40) Mg(105)* 0.9 5E B(60) Stearic (40) Mg (100) 0.85 A - ethylene, 14.8%normal butyl acrylate, 8.3% acrylic acid B - ethylene, 14.9% normalbutyl acrylate, 10.1% acrylic acid *indicates that cation was sufficientto neutralize 105% of all the acid in the resin and the organic acid.

These compositions were molded into 1.53-inch spheres for which data ispresented in the following table.

TABLE IV Sample Atti Compression COR @ 125 ft/s 1A 75 0.826 2B 75 0.8263C 78 0.837 4D 76 0.837 5E 97 0.807

Further testing of commercially available highly neutralized polymersHNP1 and HNP2 had the following properties.

TABLE V Material Properties HNP1 HNP2 Specific Gravity (g/cm³) 0.9660.974 Melt Flow, 190° C., 10-kg load 0.65 1.0 Shore D Flex Bar (40 hr)47.0 46.0 Shore D Flex Bar (2 week) 51.0 48.0 Flex Modulus, psi (40 hr)25,800 16,100 Flex Modulus, psi (2 week) 39,900 21,000 DSC Melting Point(° C.) 61.0 61/101 Moisture (ppm) 1500 4500 Weight % Mg 2.65 2.96

TABLE VI Solid Sphere Data HNP1a/HNP2a Material HNP1 HNP2 HNP2a HNP1a(50:50 blend) Spec. Grav. 0.954 0.959 1.153 1.146 1.148 (g/cm³) FillerNone None Tungsten Tungsten Tungsten Compression 107 83 86 62 72 COR0.827 0.853 0.844 0.806 0.822 Shore D 51 47 49 42 45 Shore C 79 72 75

These materials are exemplary examples of the preferred center and/orcore layer compositions of the present invention. They may also be usedas a cover layer herein.

Golf balls made with such cores enjoy high COR at relatively low clubspeeds. The COR of these balls is higher than the COR of similar ballswith higher compression cores at relatively low club speeds. At higherclub speeds, however, the COR of golf balls with low compression corescan be lower than the COR of balls with higher compression cores. Asillustrated herein, a first golf ball with a 1.505-inch core and a corecompression of 48 (hereinafter “Sample-48”) and a second golf ball witha 1.515-inch core and a core compression of 80 (hereinafter “Sample-80”)were subject to the following distance and COR tests. Sample-48 andSample-80 have essentially the same size core and similar dual-layercover. The single most significant difference between these two balls isthe compression of the respective cores.

TABLE VII Ball Speed (ft/s) Average Standard Pro 167 Big Pro 175Compression Driver Set- Driver Set- Driver Set- Driver Set- z On Ball upup up up Sample-48 86 141.7 162.3 167.0 175.2 Sample-80 103 141.5 162.1168.9 176.5 Coefficient of Restitution (COR) 200-gram 199.8-gramCompression Mass Plate Mass Plate Solid Plate Calibration z On Ball (125ft/s) (160 ft/s) (160 ft/s) Plate (160 ft/s) Sample-48 86 0.812 0.7640.759 0.818 Sample-80 103 0.796 0.759 0.753 0.836 Difference +0.016+0.005 +0.006 −0.018 (Sample-48−Sample-80)

As used in the ball speed test, the “average driver set-up” refers to aset of launch conditions, i.e., at a club head speed to which amechanical golf club has been adjusted so as to generate a ball speed ofabout 140 ft/s. Similarly, the “standard driver set-up” refers tosimilar ball speed at launch conditions of about 160 ft/s; the “Pro 167set-up” refers to a ball speed at launch conditions of about 167 ft/s;and the “Big Pro 175 set-up” refers to a ball speed at launch conditionsof about 175 ft/s. Also, as used in the COR test, the mass plate is a45-kilogram plate (100 lbs) against which the balls strike at theindicated speed. The 200-gram solid plate is a smaller mass that theballs strike and resembles the mass of a club head. The 199.8-gramcalibration plate resembles a driver with a flexible face that has a CORof 0.830.

The ball speed test results show that while Sample-48 holds a ball speedadvantage at club speeds of 140 ft/s to 160 ft/s launch conditions,Sample-80 decidedly has better ball speed at 167 ft/s and 175 ft/slaunch conditions.

Similarly, the COR test results show that at the higher collision speed(160 ft/s), the COR generally goes down for both balls, but the199.8-gram calibration test shows that the COR of the higher compressionSample-80 is significantly better than the lower compression Sample-48at the collision speed (160 ft/s). Additionally, while the COR generallygoes down for both balls, the rate of decrease is much less forSample-80 than for Sample-48. Unless specifically noted, COR values usedhereafter are measured by either the mass plate method or the 200-gramsolid plate method, i.e., where the impact plate is not flexible. Unlessotherwise noted, COR values used hereafter are measured by either themass plate method or the 200-gram solid plate method.

The intermediate layers of the present invention may, optionally,comprise a durable, low deformation material such as metal, rigidplastics, or polymers re-enforced with high strength organic orinorganic fillers or fibers, or blends or composites thereof, asdiscussed below. Suitable plastics or polymers include, but not limitedto, high cis- or trans-polybutadiene, one or more of partially or fullyneutralized ionomers including those neutralized by a metal ion sourcewherein the metal ion is the salt of an organic acid, polyolefinsincluding polyethylene, polypropylene, polybutylene and copolymersthereof including polyethylene acrylic acid or methacrylic acidcopolymers, or a terpolymer of ethylene, a softening acrylate classester such as methyl acrylate, n-butyl-acrylate or iso-butyl-acrylate,and a carboxylic acid such as acrylic acid or methacrylic acid (e.g.,terpolymers including polyethylene-methacrylic acid-n or iso-butylacrylate and polyethylene-acrylic acid-methyl acrylate, polyethyleneethyl or methyl acrylate, polyethylene vinyl acetate, polyethyleneglycidyl alkyl acrylates). Suitable polymers also include metallocenecatalyzed polyolefins, polyesters, polyamides, non-ionomericthermoplastic elastomers, copolyether-esters, copolyether-amides, EPR,EPDM, thermoplastic or thermosetting polyurethanes, polyureas,polyurethane ionomers, epoxies, polycarbonates, polybutadiene,polyisoprene, and blends thereof. In the case of metallocenes, thepolymer may be cross-linked with a free radical source, such asperoxide, or by high radiation.

Preferably, when the intermediate layer is made with polybutadiene orother synthetic and natural rubber, the rubber composition is highlycross-linked with at least 50 phr of a suitable co-reaction agent, whichincludes a metal salt of diacrylate, dimethacrylate or monomethacrylate. Preferably, the co-reaction agent is zinc diacrylate.

If desired, the golf ball can include highly rigid materials, such ascertain metals, which include, but are not limited to, tungsten, steel,titanium, chromium, nickel, copper, aluminum, zinc, magnesium, lead,tin, iron, molybdenum and alloys thereof. Suitable highly rigidmaterials include those listed in U.S. Pat. No. 6,244,977, which isincorporated by reference. Fillers with very high specific gravity, suchas those disclosed in U.S. Pat. No. 6,287,217, which is incorporated byreference, can also be incorporated into the inner core. Suitablefillers and composites include, but not limited to, carbon includinggraphite, glass, aramid, polyester, polyethylene, polypropylene, siliconcarbide, boron carbide, natural or synthetic silk.

In accordance to one embodiment of the present invention, the golf ballcomprises at least two core layers, an innermost core and an outer core,and a cover. Preferably, outer core comprises a flexible, lowcompression, high COR rubber composition discussed above, and inner corecomprises a low deformation material discussed above. The hard, lowdeformation inner core resists deformation at high club speeds tomaintain the COR at an optimal level, while the resilient outer layerprovides high COR at slower club speeds and the requisite softness forshort iron club play. The inventive ball, therefore, enjoys high initialvelocity and high COR at high and low club head speeds associated, whilemaintaining a desirable soft feel and soft sound for greenside play.

Other rubber compounds for outer core may also include any lowcompression, highly resilient polymers comprising natural rubbers,including cis-polyisoprene, trans-polyisoprene or balata, syntheticrubbers including 1,2-polybutadiene, cis-polybutadiene,trans-polybutadiene, polychloroprene, poly(norbornene), polyoctenamerand polypentenamer among other diene polymers. Outer core may comprise aplurality of layers, e.g., a laminate, where several thin flexiblelayers are plied or otherwise adhered together.

Preferably, the rigid inner core, if present, has a flexural modulus inthe range of about 25,000 psi to about 250,000 psi. More preferably, theflexural modulus of the rigid inner core is in the range of about 75,000psi to about 225,000 psi, and most preferably in the range of about80,000 psi to about 200,000 psi. Furthermore, the rigid inner core hasdurometer hardness in the range of greater than about 70 on the Shore Cscale. The compression of the rigid inner core is preferably in therange of greater than about 60 PGA or Atti. More preferably, thecompression is greater than about 70, and most preferably greater thanabout 80. Shore hardness is measured according to ASTM D-2240-00, andflexural modulus is measured in accordance to ASTM D6272-98 about twoweeks after the test specimen are prepared.

Preferably, the outer core is softer and has a lower compression thanthe inner core. Preferably, outer core has a flexural modulus of about500 psi to about 25,000 psi. More preferably, the flexural modulus isless than about 15,000 psi. The outer core preferably has a hardness ofabout 25 to about 70 on the Shore C scale. More preferably, the hardnessis less than 60 on the Shore C scale.

One preferred way to achieve the difference in hardness between theinner core and the outer core is to make the inner core from un-foamedpolymer, and to make the outer core from foamed polymer selected fromthe suitable materials disclosed herein. Alternatively, the outer coremay be made from these suitable materials having their specific gravityreduced. In this embodiment the inner and outer core can be made fromthe same polymer or polymeric composition.

Preferably, outer core layer has a thickness from about 0.001 inches toabout 0.100 inches, preferably from bout 0.010 inches to about 0.050inches and more preferably from about 0.015 inches to about 0.035inches. Preferably, the overall core diameter is greater than about 1.50inches, preferably greater than about 1.580 inches, and more preferablygreater than about 1.60 inches. The inner core may have any dimension solong as the overall core diameter has the preferred dimensions listedabove.

The cover should be tough, cut-resistant, and selected from conventionalmaterials used as golf ball covers based on the desired performancecharacteristics. The cover may be comprised of one or more layers. Covermaterials such as ionomer resins, blends of ionomer resins,thermoplastic or thermoset urethane, and balata, can be used as known inthe art.

The cover is preferably a resilient, non-reduced specific gravity layer.Suitable materials include any material that allows for tailoring ofball compression, coefficient of restitution, spin rate, etc. and aredisclosed in U.S. Pat. Nos. 6,419,535; 6,152,834; 5,919,100; and5,885,172, which is incorporated by reference. Ionomers, ionomer blends,thermosetting or thermoplastic polyurethanes, metallocenes,polyurethanes, polyureas (and hybrids thereof), are the preferredmaterials. The cover can be manufactured by a casting method, reactioninjection molded, injected or compression molded, sprayed or dippedmethod. Preferably the cover is cast about the core.

In a preferred embodiment, the golf ball includes an intermediate layer,as either an outer core layer or an inner cover, in addition to theouter cover. As disclosed in the U.S. Pat. Nos. 5,885,172 and 6,132,324,which are incorporated herein by reference in their entireties, outercover layer is made from a soft thermoset material, such as castpolyurethane or polyurea, and inner cover is made from an ionomericmaterial, preferably including at least two ionomers.

When the intermediate layer is an inner cover layer, it is preferablyformed from a high flexural modulus material which contributes to thelow spin, distance characteristics of the presently claimed balls whenthey are struck for long shots (e.g. driver or long irons).Specifically, the inner cover layer materials have a Shore D hardness ofabout 55 or greater, preferably about 55-70 and most preferably about60-70. The flexural modulus of intermediate cover layer is at leastabout 50,000 psi, preferably about 50,000 psi to about 150,000 psi andmost preferably about 75,000 psi to about 125,000 psi. In the preferredembodiment, the intermediate layer has a thickness of from about 0.1inches to about 0.5 inches, more preferably between about 0.11 inchesand about 0.12 inches, and most preferably between about 0.115 inchesand about 0.119 inches. In another thin-layer embodiment, he thicknessof the intermediate layer can range from about 0.020 inches to about0.045 inches, preferably about 0.030 inches to about 0.040 inches andmost preferably about 0.035 inches.

Outer cover layer is formed preferably from a relatively soft thermosetmaterial in order to replicate the soft feel and high spin playcharacteristics of a balata ball for “short game” shots. In particular,the outer cover layer should have Shore D hardness of less than 65 orfrom about 40 to about 64, preferably 40-60 and most preferably 40-50.Additionally, the materials of the outer cover layer must have a degreeof abrasion resistance in order to be suitable for use as a golf ballcover. The outer cover layer of the present invention can comprise anysuitable thermoset or thermoplastic material, preferably which is formedfrom a castable reactive liquid material. The preferred materials forthe outer cover layer include, but are not limited to, thermoseturethanes and polyurethanes, thermoset urethane ionomers and thermoseturethane epoxies. Examples of suitable polyurethane ionomers aredisclosed in U.S. Pat. No. 5,692,974 entitled “Golf Ball Covers,” thedisclosure of which is hereby incorporated by reference in its entiretyin the present application. Thermoset polyurethanes and polyureas arepreferred for the outer cover layers of the balls of the presentinvention.

In accordance with another embodiment of the present invention, the golfball comprises a relatively small, low compression, high COR inner core.The diameter of the inner core (or center) is preferably less than 1.40inches or smaller, more preferably 0.8 inches to about 1.4 inches, andmost preferably from about 1.3 inches to about 1.4 inches. The desiredthickness of either the core (center) or intermediate layer can beselected in conjunction with the flexural modulus of the material of thelayers and the desired overall compression of the ball and deformationof the ball.

Most preferably, inner core is formed from a rubber compositioncontaining a halogenated thiophenol compound. Such halogenatedthiophenol compounds are fully disclosed in commonly owned andco-pending '963 and '448 patent applications, which have alreadyincorporated by reference and discussed above. In accordance to oneaspect of the second embodiment, the rubber compound preferably is ahigh cis- or trans- polybutadiene and has a viscosity of about 40 Mooneyto about 60 Mooney. The core has a hardness of greater than about 70 onthe Shore C scale, and preferably greater than 80 on the Shore C scale.The core also has a compression of less than about 60 PGA, and morepreferably less than about 50 PGA. The resulting core exhibits a COR ofat least about 0.790, and most preferably at least 0.800 at 125 ft/s.Other suitable polymers for inner core include a polyethylene copolymer,EPR, EPDM, a metallocene catalyzed polymer or any of the materialsdiscussed above in connection with outer core discussed above, so longas the preferred compression, hardness and COR are met.

Inner core may be encased by outer core layers comprising the samematerials or different compositions than inner core. These outer corelayers may be laminated together. Each of the laminate layers preferablyhas a thickness from about 0.001 inches to about 0.100 inches and morepreferably from about 0.010 inches to about 0.050 inches.

Preferably, the intermediate layer is made from a low deformationpolymeric material, such as an ionomer, including low and high acidionomer, any partially or fully neutralized ionomer or any thermoplasticor thermosetting polymer. The intermediate layer preferably has aflexural modulus of greater than 50,000 psi and more preferably greaterthan 75,000 psi. Among the preferred materials are hard, high flexuralmodulus ionomer resins and blends thereof. Additionally, other suitablemantle materials (as well as core and cover materials) are disclosed inU.S. Pat. No. 5,919,100 and international publications WO 00/23519 andWO 01/29129. These disclosures are incorporated by reference herein intheir entireties. One particularly suitable material disclosed in WO01/29129 is a melt processible composition comprising ahighly-neutralized ethylene copolymer and one or more aliphatic,mono-functional organic acids having fewer than 36 carbon atoms of saltsthereof, wherein greater than 90% of all the acid of the ethylenecopolymer is neutralized.

These ionomers are obtained by providing a cross metallic bond topolymers of monoolefin with at least one member selected from the groupconsisting of unsaturated mono- or di-carboxylic acids having 3 to 12carbon atoms and esters thereof (the polymer contains 1 to 50% by weightof the unsaturated mono- or di-carboxylic acid and/or ester thereof).More particularly, such acid-containing ethylene copolymer ionomercomponent includes E/X/Y copolymers where E is ethylene, X is asoftening comonomer such as acrylate or methacrylate present in 0-50weight percent of the polymer (preferably 0-25 wt. %, most preferably0-20 wt. %), and Y is acrylic or methacrylic acid present in 5-35 weightpercent of the polymer (preferably at least about 16 wt. %, morepreferably at least about 16-35 16 wt. %, most preferably at least about16-20 16 wt. %), wherein the acid moiety is neutralized 1-90%(preferably at least 40%, most preferably at least about 60%) to form anionomer by a cation such as lithium*, sodium*, potassium, magnesium*,calcium, barium, lead, tin, zinc* or aluminum (*=preferred), or acombination of such cations. Specific acid-containing ethylenecopolymers include ethylene/acrylic acid, ethylene/methacrylic acid,ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylicacid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate,ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylicacid/n-butyl methacrylate, ethylene/acrylic acid/methyl methacrylate,ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/methacrylic acid/methyl methacrylate, andethylene/acrylic acid/n-butyl methacrylate. Preferred acid containingethylene copolymers include ethylene/methacrylic acid, ethylene/acrylicacid, ethylene/methacrylic acid/n-butyl acrylate, ethylene/acrylicacid/n-butyl acrylate, ethylene/methacrylic acid/methyl acrylate andethylene/acrylic acid/methyl acrylate copolymers. The most preferredacid-containing ethylene copolymers are ethylene/methacrylic acid,ethylene/acrylic acid, ethylene/(meth)acrylic acid/n-butyl acrylate,ethylene/(meth)acrylic acid/ethyl acrylate, and ethylene/(meth)acrylicacid/methyl acrylate copolymers.

The manner in which the ionomers are made is well known in the art asdescribed in e.g., U.S. Pat. No. 3,262,272. Such ionomer resins arecommercially available from DuPont under the tradename SURLYN® and fromExxon under the tradename IOTEK®. Some particularly suitable SURLYNS®include SURLYN® 8140 (Na) and SURLYN® 8546 (Li), which have amethacrylic acid content of about 19%.

Other suitable mantle materials include the low deformation materialsdescribed above and any hard, high flexural modulus, resilient materialthat is compatible with the other materials of the golf ball. Examplesof other suitable inner cover materials include thermoplastic orthermoset polyurethanes, thermoplastic or thermoset polyetheresters orpolyetheramides, thermoplastic or thermoset polyester, a dynamicallyvulcanized elastomer, a functionalized styrenebutadiene elastomer, ametallocene polymer or blends thereof.

Suitable thermoplastic polyetheresters include materials, which arecommercially available from DuPont under the tradename HYTREL®. Suitablethermoplastic polyetheramides include materials, which are availablefrom Elf-Atochem under the tradename PEBAX®. Other suitable materialsfor the inner cover layer include nylon andacrylonitrile-butadiene-styrene copolymer (ABS).

Another suitable material for the intermediate layer is a highstiffness, highly neutralized ionomer having a durometer hardness of atleast about 50 on the Shore D scale and a flexural modulus of at least50,000 psi. The flexural modulus ranges from about 50,000 psi to about150,000 psi. The hardness ranges from about 55 to about 80 Shore D, morepreferably about 55 to about 70 Shore D. This ionomer, preferably atleast two ionomers, may be blended with a lowly neutralized ionomershaving an acid content of 5 to 25%, and may be blended withnon-ionomeric polymers or compatilizers (e.g., glycidyl or maleicanhydride), so long as the preferred hardness and flexural modulus aresatisfied. Examples of highly neutralized ionomers are disclosed in U.S.Pat. No. 6,756,436 which is incorporated herein by reference.

In one preferred embodiment, this suitable material is a blend of afatty acid salt highly neutralized polymer, such as a melt processiblecomposition comprising a highly neutralized ethylene copolymer and oneor more aliphatic, mono-functional organic acids having fewer than 36carbon atoms of salts thereof, wherein greater than 90% of all the acidof the ethylene copolymer is neutralized, and a high stiffness partiallyneutralized ionomer, such as those commercially available as SURLYN®8945, 7940, 8140 and 9120, among others. This blend has hardness in therange of about 65 to about 75 on the Shore D scale.

The intermediate layer may also comprise a laminated layer, if desired.For example, the intermediate layer may comprise a laminate comprisingfour layers: a polyamide layer having a flexural modulus of about200,000 psi, a terpolymer ionomer or un-neutralized acid terpolymerhaving a flexural modulus of about 30,000 psi, a low acid ionomer havinga flexural modulus of about 60,000 psi and a high acid ionomer having aflexural modulus of about 70,000 psi. The composite flexural modulus ofthe four-layer laminate is about 90,000 psi or approximately the averageof the flexural modulus of the four layers, assuming that the thicknessof each layer is about the same.

In a preferred embodiment, inner core, if present, has a diameter ofabout 0.800 to about 1.400 inches, more preferably about 1.3 to about1.4 inches, a compression of about 44 or less, and a COR of about 0.800.The intermediate layer comprises at least two ionomers having a flexuralmodulus of about 50,000 psi or higher and has a thickness of at leastabout 0.110 inches, preferably between about 0.11 inches and about 0.12inches. The cover is preferably a cast polyurethane or polyurea having ahardness of about 40 to about 60 Shore D. The core compression ispreferably about 44 or less, and the combination of core andintermediate layer has a compression of from about 70 to about 100.

The core preferably comprises a single solid layer. Alternatively, thecore may comprise multiple layers. Preferably, its diameter is about1.400 inches or less, more preferably between about 0.8 inches and about1.4 inches, most preferably between about 1.3 inches and about 1.4inches. The core has a COR of about 0.770 or greater, more preferablyabout 0.800 or greater, and most preferably about 0.820 or greater, soas to give the ball a COR of at least 0.800 and more preferably in therange of about 0.805 to about 0.820. In one preferred embodiment, thecore has a COR of about 0.770 to about 0.810.

In a preferred embodiment, intermediate cover layer and outer coverlayer are similar to the inner cover layer and the outer cover layer ofcover, respectively, for progressive performance. For example, outercover layer is made from a soft, thermosetting polymer, such as castpolyurethane, and intermediate cover layer is made from a rigid ionomeror similar composition having hardness of at least 55 on the Shore Dscale and flexural modulus of at least 55,000 psi.

The total thickness the cover is preferably less than 0.125 inches.Innermost layer preferably is about 0.005 inches to about 0.100 inchesthick, more preferably 0.010 inches to about 0.090 inches, and mostpreferably about 0.015 inches to about 0.070 inches. Intermediate coverlayer preferably is about 0.010 inches to about 0.050 inches thick, andouter cover layer preferably is about 0.020 inches to about 0.040 inchesthick.

While any of the embodiments herein may have any known dimple number andpattern, a preferred number of dimples is 252 to 456, and morepreferably is 330 to 392. The dimples may comprise any width, depth, andedge angle disclosed in the prior art and the patterns may comprisesmultitudes of dimples having different widths, depths and edge angles.The parting line configuration of said pattern may be either a straightline or a staggered wave parting line (SWPL). Most preferably the dimplenumber is 330, 332, or 392 and comprises 5 to 7 dimples sizes and theparting line is a SWPL.

Golf balls made in accordance to the present invention and disclosedabove have a compression of greater than about 60 PGA, more preferablygreater than about 80 and even more preferably greater than about 90PGA. These balls exhibit COR of at least 0.80 at 125 ft/s and morepreferably at least 0.81 at 125 ft/s. These balls also exhibit COR of atleast 0.75 at 160 ft/s and more preferably at least 0.76 at 160 ft/s.

All patents and patent applications cited in the foregoing text areexpressly incorporated herein by reference in their entirety.

The invention described and claimed herein is not to be limited in scopeby the specific embodiments herein disclosed, since these embodimentsare intended as illustrations of several aspects of the invention. Anyequivalent embodiments are intended to be within the scope of thisinvention. Indeed, various modifications of the invention in addition tothose shown and described herein will become apparent to those skilledin the art from the foregoing description. Such modifications are alsointended to fall within the scope of the appended claims.

1. A golf ball comprising: a low compression core having an outersurface and a geometric center and being formed from a substantiallyhomogenous composition throughout, the core having a diameter of 1.18inches to 1.40 inches, an Atti compression of 42 or less, and acoefficient of restitution of 0.750 to 0.790; and an outer cover havinga thickness of 0.14 inches to 0.16 inches and having a Shore D hardnessof 60 to 70; wherein the outer surface has a first hardness and thegeometric center has a second hardness, the first hardness beingsubstantially the same as or lower than the second hardness.
 2. The golfball of claim 1, wherein the core compression is 20 or less.
 3. The golfball of claim 1, wherein the second hardness is about 0 Shore C to about5 Shore C higher than the first hardness.
 4. The golf ball of claim 1,wherein the core has a maximum hardness value and the second hardness isless than about 10 Shore C from the maximum hardness value.
 5. The golfball of claim 4, wherein the second hardness is less than about 5 ShoreC from the maximum hardness value.
 6. A golf ball comprising: a lowcompression core having a substantially homogenous compositionthroughout, an outer surface, and a geometric center, the core having adiameter of 1.20 inches to 1.36 inches, a compression of 30 or less, anda coefficient of restitution of 0.750 to 0.790 when measured at anincoming velocity of 125 ft/s; and an outer cover having a thickness of0.125 inches to 0.200 inches; wherein the geometric center has a firsthardness, the outer surface has a second hardness, and the core has amaximum hardness, the first hardness being substantially the same as orhigher than the second hardness and is less than about 10 Shore C lowerthan the maximum hardness.
 7. The golf ball of claim 6, wherein thefirst hardness is less than about 5 Shore C lower than the maximumhardness.
 8. The golf ball of claim 6, wherein the second hardness isabout 0 Shore C to about 10 Shore C lower than the first hardness. 9.The golf ball of claim 8, wherein the second hardness is about 0 Shore Cto about 5 Shore C lower than the first hardness.
 10. The golf ball ofclaim 6, wherein the core has a compression of 20 or less.
 11. The golfball of claim 10, wherein the core has a compression of 10 or less. 12.The golf ball of claim 6, wherein the composition further comprises asoft and fast agent
 13. A golf ball comprising: a low compression corehaving a substantially homogenous thermoset rubber compositionthroughout, an outer surface having a first hardness, and a centerhaving a second hardness, the first hardness being substantially thesame as or lower than the second hardness to define a negative hardnessgradient; and an outer cover having a thickness of 0.125 inches to 0.200inches; wherein the core comprises a diene rubber composition, has anouter diameter of 1.18 inches to 1.40 inches, a compression of 30 orless, and a coefficient of restitution of 0.750 to 0.790 when measuredat an incoming velocity of 125 ft/s, and wherein the golf ball has acompression of 75 to 110 and a coefficient of restitution of 0.810 orgreater when measured at an incoming velocity of 125 ft/s.
 14. The golfball of claim 13, wherein the core has a diameter of 1.2 inches to 1.36inches and a compression of 20 or less.
 15. The golf ball of claim 14,wherein the core compression is 10 or less.
 16. The golf ball of claim13, wherein the core has a maximum hardness and the second hardness isless than about 5 Shore C lower than the maximum hardness.
 17. The golfball of claim 13, wherein the second hardness is about 0 Shore C toabout 10 Shore C lower than the first hardness.
 18. The golf ball ofclaim 17, wherein the second hardness is about 0 Shore C to about 5Shore C lower than the first hardness.
 19. The golf ball of claim 13,wherein the cover has a hardness of 70 Shore D or less.
 20. The golfball of claim 13, wherein the cover thickness is 0.14 inches to 0.16inches.